Polymer Synthesis
CHEM 421
Free Radical
Polymerizations
Polymer Synthesis
CHEM 421
Reading assignments:
Chapter 3-3, 3-4, 3-5, 3-8 (Odian)
Free Radical Solution
Polymerizations
Polymer Synthesis
CHEM 421
• Initiation
kd
I
2 R
d [R•] / dt = 2 kd [I]
= 2 f kd [I]
R
+
ki
M
R
M
- d [R•] / dt = ki [R•] [M]
• Propagation
R M
+ nM
ki
Pn M
rp = kp [M•] [M]
• Termination
Pn
+
Pm
kt
Dead Polymer
- d [P•] / dt = 2 kt [P•]2
Free Radical Solution
Polymerizations
• Overall rate expression
–Assumptions?
Rp = kp [M] [M•]
» Steady State Approximation (Ri = Rt)
2 f kd [I] = 2 kt [M•]2
[M•] = (kd f [I] / kt)1/2
Rp = kp [M] (kd f [I] / kt)1/2
Polymer Synthesis
CHEM 421
Free Radical Solution
Polymerizations
• Overall rate expression
Rp = kp [M] (kd f [I] / kt)1/2
–Rate is first order in monomer
–Rate is ½ order in initiator
• To increase Rp
Polymer Synthesis
CHEM 421
Determination of Orders of Reaction Polymer Synthesis
T =75 C, P= 4000 psig, CO2 = 0.74 g/ml
CHEM 421
Rp = ([VF2]IN-[VF2]OUT)/
2 .5 E -0 4
2 .5 E -0 4
[DEPDC]IN =3 mM
Rp (mol/L x sec)
2 .0 E -0 4
2 .0 E -0 4
1 .5 E -0 4
1 .5 E -0 4
I*
1 .0 E -0 4
1 .0 E -0 4
5 .0 E -0 5
5 .0 E -0 5
0 .0 E + 0 0
0 .0 E + 0 0
0
0 .5
1
1 .5
2
0
0 .0 1
[VF2]out (mol/L)
 Rp  kp [Iout-I*] 0.5 [VF2]out1.0
0 .0 2
[I]out
0 .0 3
0.5
0 .0 4
(mol/L)
0 .0 5
Experimental Ways of
Determining Rp
Polymer Synthesis
CHEM 421
• Separation and isolation of product
–Precipitation
–Chromatography
• Chemical analysis
–Titration of un-reacted double bonds…
• Spectroscopic methods
–UV/Vis, NMR, FTIR
• Refractive index changes
• Dilatometry
• Calorimetry
React-IR
Polymer Synthesis
CHEM 421
t = 30 s, 32 scans
reaction conditions: p = 5000 p.s.i., T = 35 °C, 73 mol-% PDD in feed
phase separation  emulsion
Dilatometer
Polymer Synthesis
CHEM 421
Free Radical Solution
Polymerizations
• Overall rate expression
Rp = kp [M] (kd f [I] / kt)1/2
–Rate is first order in monomer
–Rate is ½ order in initiator
• Qualitative picture…?
Polymer Synthesis
CHEM 421
Free Radical Solution
Polymerizations
Polymer Synthesis
CHEM 421
• Kinetic Chain Length (٧)
–Average number of monomer units
polymerized per chain initiated
Rp
Rp
Ri
Rt
٧= — = —
kp [M] [M•]
kp [M]
kp [M]
٧ = ————
=
———
=
—————
2 (kt kd f [I])1/2
2 kt [M•]2
2 kt [M•]
Free Radical Solution
Polymerizations
• Kinetic Chain Length (٧)
kp [M]
٧ = —————
2 (kt kd f [I])1/2
–To increase molecular weight…
–To increase Rate of Polymerization
Polymer Synthesis
CHEM 421
Kinetic Chain Length (٧) vs
Degree of Polymerization (DP)
• Termination by combination
DP = 2٧
• Termination by disproportionation
DP = ٧
Polymer Synthesis
CHEM 421
Polymer Synthesis
CHEM 421
Classes of Free Radical
Initiators
Polymer Synthesis
CHEM 421
Initiator Decompositions
Polymer Synthesis
CHEM 421
• Differences in the decomposition rates of various
initiators can be expressed in terms of initiator half life
• The rate of initiator disappearance is: - d[I] / dt = kd [I]
• Integrate:
[I] = [I]0 e-k t
d
[I]0
log —— = kdt
[I]
or
• Half life?
[I]0
set: [I] = ——
2
t1/2
0.63
= ———
kd
Polymer Synthesis
CHEM 421
Factors which Influence
Initiator Choice
Polymer Synthesis
CHEM 421
• Temperature of polymerization
• Solubility of the initiator
• End group control or functionalization
HO
OH
+
Termination by combination
HO
PBd
OH
Factors which Influence
Initiator Choice
Polymer Synthesis
CHEM 421
• End group control or functionalization
O
O
K
S
O
O
CF2
CF2
CF2
CF
CF2
O
CF
O
O
O
O
OCF3
S
K
CF2CF2CF2CF2Br
F3CF2CF2C
CF2
CF2
CF2
CF
OCF3
CF2
CF
CF2CF2CF3
O
CF2CF2CF2CF2Br
Pulsed-laser Polymerization in
Polymer Synthesis
Homogeneous Phase: Determination of kp CHEM 421
Pulsed-laser Polymerization in
Polymer Synthesis
Homogeneous Phase: Determination of kp CHEM 421
Evaluation of kp
Polymer Synthesis
CHEM 421
Kinetic Chain Length Profile
in a PLP Experiment
Polymer Synthesis
CHEM 421
Li=i kp [M] td
Polymer Synthesis
CHEM 421
Li=i kp [M] td
Polymer Synthesis
CHEM 421